We use this tool in our CI infrastructure for installing test packages; we don't want to run apt-get update to install testpackages because you might end up installing install packages that are newer than what is supposed to be on the image, giving you an unknown image package configuration on the image.

If we want to use phablet-config also for convenience, we could add a flag that forces to run apt-get update before installing packages.

There is no "convenience" here. If you don't update you can't install any packages unless you have the very latest image when it comes out . You get 404 errors because the package cache is out of date.

The problem of not updating the archive index is that it might not be able to find the desirable packages, which is a valid problem.

If the testing tool really want to make sure a specific version is installed, it should force that instead. We're just lucky here that we didn't have issues with this, as I believe we're always testing a fresh image. At the moment we decide to test an older image, we'll get 404 errors.

We can hold this fix, but it'd be nice if we could improve our CI tools to do the right thing instead.